1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by means of a perpendicular magnetic recording system, and more specifically, to a magnetic head for perpendicular magnetic recording that has a main pole and a shield, and a method of manufacturing the same.
2. Description of Related Art
The recording systems of magnetic read/write apparatuses include a longitudinal magnetic recording system wherein signals are magnetized in a direction along the plane of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in a direction perpendicular to the plane of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density, compared with the longitudinal magnetic recording system.
Magnetic heads for perpendicular magnetic recording typically have, like those for longitudinal magnetic recording, a structure where a read head having a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head having an induction-type electromagnetic transducer for writing are stacked on a substrate. The write head includes a main pole that produces a magnetic field in a direction perpendicular to the plane of the recording medium. The main pole includes, for example, a track width defining portion having an end located in a medium facing surface that faces the recording medium, and a wide portion that is connected to the other end of the track width defining portion and is greater in width than the track width defining portion. The track width defining portion has a generally constant width. To achieve higher recording density, it is required that the write head of the perpendicular magnetic recording system be smaller in track width and improved in write characteristics such as overwrite property which is a parameter indicating an overwriting capability.
A magnetic head for use in a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the medium facing surface mentioned above. The medium facing surface has an air inflow end and an air outflow end. The slider is designed to slightly fly over the surface of the recording medium by means of an airflow that comes from the air inflow end into the space between the medium facing surface and the recording medium. The magnetic head is typically disposed near the air outflow end of the medium facing surface of the slider. In a magnetic disk drive, positioning of the magnetic head is performed by a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit about the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs according to the position of the magnetic head across the tracks.
In particular, in a magnetic disk drive of the perpendicular magnetic recording system which is higher in capability of writing on a recording medium than the longitudinal magnetic recording system, the skew mentioned above can cause the phenomenon that signals already written on one or more tracks that are adjacent to a track targeted for writing are erased or attenuated during writing of a signal on the track targeted for writing (such a phenomenon will hereinafter be referred to as adjacent track erase). To increase the recording density, it is required to prevent the occurrence of adjacent track erase.
One known technique for preventing the skew-induced adjacent track erase is to form the main pole such that its end face located in the medium facing surface has a width that decreases with increasing proximity to the top surface of the substrate, as described in U.S. Patent Application Publication No. 2005/0141137 A1, U.S. Patent Application Publication No. 2007/0177301 A1, and U.S. Pat. No. 6,954,340 B2, for example.
Another effective technique for preventing the skew-induced adjacent track erase is to provide two side shields on opposite sides of the main pole in the track width direction, as described in U.S. Patent Application Publication No. 2005/0141137 A1 and U.S. Patent Application Publication No. 2007/0177301 A1. It is also effective to provide a shield having an end face that is located in the medium facing surface and wraps around the end face of the main pole (such a shield will hereinafter be referred to as a wrap-around shield), as described in U.S. Pat. No. 6,954,340 B2. The wrap-around shield includes a bottom shield that is located on the air-inflow-end side relative to the main pole, a top shield that is located on the air-outflow-end side relative to the main pole, and two side shields that are located on opposite sides of the main pole in the track width direction. The aforementioned techniques make it possible to capture a magnetic flux that is produced from the end face of the main pole and spreads out in the track width direction. It is thereby possible to prevent the occurrence of adjacent track erase.
A main pole that is shaped such that its end face located in the medium facing surface decreases in width with increasing proximity to the top surface of the substrate has the following problem. If the main pole of such a shape is formed by a conventional method of forming a main pole, a major part of the side surface of the main pole along the entire perimeter of the main pole is formed into a tilt surface tilted with respect to a direction perpendicular to the top surface of the substrate. This makes the main pole smaller in cross-sectional area perpendicular to the direction of flow of the magnetic flux, as compared with a case where the entire side surface of the main pole is perpendicular to the top surface of the substrate. Such a main pole cannot allow much magnetic flux to pass, especially through a part near the boundary between the track width defining portion and the wide portion. This results in degradation of write characteristics such as overwrite property.
An effective approach to the aforementioned problem is, as disclosed in U.S. Patent Application Publication No. 2008/0239567 A1, to form the main pole into the following shape. The main pole formed by the technique disclosed therein has first and second side surfaces that are opposite to each other and located in a first region extending from the medium facing surface to a position at a predetermined distance from the medium facing surface, and third and fourth side surfaces that are located in a second region other than the first region. The main pole further has a fifth side surface located in the boundary between the first and second regions and connecting the first side surface to the third side surface, and a sixth side surface located in the boundary between the first and second regions and connecting the second side surface to the fourth side surface. The distance between the first side surface and the second side surface in the track width direction decreases with increasing proximity to the top surface of the substrate. In the boundary between the first region and the second region, the distance between the third side surface and the fourth side surface in the track width direction as seen at the position closest to the top surface of the substrate is greater than the distance between the first side surface and the second side surface in the track width direction as seen at the position closest to the top surface of the substrate. Each of the fifth and sixth side surfaces has a width that increases with increasing proximity to the top surface of the substrate. This technique allows the main pole to have a large cross-sectional area perpendicular to the direction of flow of the magnetic flux in the vicinity of the boundary between the track width defining portion and the wide portion, thereby allowing much magnetic flux to pass. This makes it possible to improve write characteristics such as overwrite property.
Here, a magnetic head that is configured to have a main pole of the above-described shape and two side shields will be contemplated. The two side shields have respective sidewalls that are opposed to two side parts of the main pole. In order for the two side shields to sufficiently capture a magnetic flux that is produced from the end face of the main pole and spreads out to opposite areas in the track width direction, it is preferred that the distance from the side parts of the main pole to the sidewalls of the side shields be small and constant in the medium facing surface.
If the sidewalls of the side shields are opposed to the side parts of the main pole at a small distance therefrom over a wide area except the medium facing surface, flux leakage from the main pole to the side shields will increase to cause degradation of write characteristics such as overwrite property. To avoid this, the side shields might be reduced in dimension in the direction perpendicular to the medium facing surface. Such a reduction in dimension, however, makes the side shields smaller in volume and thus impairs the original function of the side shields.